Dielectrophoretic tweezers apparatus and methods

ABSTRACT

Dielectrophoretic (DEP) tweezers apparatus and methods for various applications, including particle trapping. Multiple electrodes (e.g., two or three) are disposed on or otherwise constitute an elongated object forming a tip. Exemplary electrode configurations include, but are not limited to, coaxial and triaxial arrangements. A voltage is applied across these electrodes to produce a non-uniform electromagnetic field proximate to the tip thereby creating a dielectrophoretic trap. Once trapped, a particle may be moved to desired locations via manipulation of the elongated object or the medium in which the particle is located. Multiple DEP tweezers apparatus may be arranged to form arrays of tips capable of respectively generating local electromagnetic fields confined to the tips. Such DEP arrays may be employed in nanofabrication processes involving nanolithography or nano-manipulation, as well as data storage and retrieval applications.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims the benefit, under 35 U.S.C. § 119(e), to U.S. provisional application Ser. No. 61/031,523, filed Feb. 26, 2008, entitled “Dielectrophoretic Tweezers Apparatus and Methods,” which application is hereby incorporated herein by reference.

GOVERNMENT SPONSORED RESEARCH

Some of the research relating to the subject matter disclosed herein was sponsored by one or both of U.S. government grants NSF/PHY 01-17795 and NSF-PHY-06-46094, and the government has certain rights to at least some disclosed subject matter.

BACKGROUND

It is well known that particles (e.g., atoms, molecules, cells) may have non-uniform concentrations of positive and negative charge. For instance, a molecule is made of multiple atoms that each include a positively charged center region known as a nucleus and a varying number of negatively charged subatomic particles known as electrons that exist in an outer negatively charged region around the nucleus. When the atoms combine to form the molecule, the forces associated with these two charged regions bind the atoms together. The shape of the molecule may result in a nonuniform distribution of charge, thereby producing respective concentrations of positive charge and negative charge. When this occurs, the molecule is called a polar or polarized molecule. Polarity can be induced in an otherwise non-polar molecule. Specifically, when a normally non-polar molecule is placed in a strong electromagnetic field, the negatively charged electrons are sometimes separated from the positively charged nuclei so that the otherwise non-polar molecule becomes polarized. For the purposes of the present disclosure, the terms “polar” or “polarized” are used to describe any particles that are naturally polar as well as any particles that are made polar by applying an electromagnetic field.

Since one region of a polar molecule is more positively charged and another region is more negatively charged, a force is exerted on such a molecule when it is placed into a non-uniform electromagnetic field (an electromagnetic field in which the field strength varies from one location to another). This force, known as a dielectric force, can cause the molecule to move. The exact direction of movement and velocity at which the molecule moves depends upon the particular characteristics of the molecule, the medium in which the molecule is located, and the electromagnetic field.

Specialized microscopes referred to as Scanning Probe Microscopes (SPMs) can be used to probe molecules on a scale of nanometers. One type of SPM is the Atomic Force Microscope (AFM). An AFM comprises a cantilever having a tip on one end that is scanned across a sample. Very small movements of the tip, based on variations in the profile of the surface of the sample over which the tip is scanned, are typically measured by a laser detection system and are used to generate an image of the surface profile of the scanned sample.

In some instances, the tip of an SPM need not actually make contact with the sample surface to be imaged. For example, in U.S. Pat. No. 5,936,237 to van der Weide, an SPM tip is configured as a conductor with a conducting shield around it. This configuration allows the SPM to perform a non-contact scan of a sample surface to provide an image of the surface profile based on electromagnetic field interaction between the tip and the surface. During such a scan, because no insulator separates the conducting tip from the sample, a distance is maintained between the sample and the conducting tip.

Another device commonly used with small particles is a micromanipulator. Micromanipulators are devices that move tools which are used to probe and manipulate samples on a cellular scale. Micromanipulators are used, for example, for microsurgery and other biological purposes. A micropipette is one example of a tool that can be used to probe and manipulate samples in connection with a micromanipulator. An optical microscope capable of viewing individual cells can be used to directly view a sample being manipulated by a tool coupled to a micromanipulator (hereinafter referred to as a “micromanipulator tool”).

SUMMARY

The present disclosure relates generally to methods and apparatus for generating a dielectrophoretic force proximate to a tip, such as an SPM tip or micromanipulator tool tip. A tip generating such a force can then be positioned near a target particle in order to exert a force on that particle in such a way as to trap the particle (thereby creating a dielectrophoretic trap). Once a target particle is in this trap, it may be held there as long as the electromagnetic field that gives rise to the dielectrophoretic force is being generated. A tip thusly configured forms a “dielectrophoretic (DEP) tweezers.”

According to some inventive embodiments of the present disclosure discussed in greater detail below, a non-uniform electromagnetic field giving rise to a dielectrophoretic force at an end of a tip is created by a pair of electrodes integrated with the tip to form a DEP tweezers apparatus. These electrodes can take many forms. For example, in one possible embodiment, an SPM tip itself (e.g., an AFM tip), formed of an electrically conductive material, forms a first electrode, and an insulating layer and a second electrode are placed around the tip in a coaxial configuration. An electromagnetic field providing a dielectrophoretic force proximate to the end of the tip can then be generated by applying a voltage across these first and second electrodes. The voltage can be turned on and off as desired so as to selectively trap one or more target particles.

In one inventive embodiment, such “coaxial” DEP tweezers apparatus can be used to trap and move small dielectric objects in a fluid using positive dielectrophoresis (pDEP). As noted above, in one exemplary implementation, a coaxial DEP tweezers apparatus may be fabricated by coating a conducting tip with a thin insulating layer, followed by a thin metal film forming an outer shell. The end of the tip may be opened up with a focused ion beam. When an RF voltage is applied between the conducting tip and the grounded outer shell, a sharp maximum in electric field amplitude is created just at the end of the tip. This attracts objects that have a larger dielectric constant than the fluid (e.g., such a tip attracts biological cells in water).

In another inventive embodiment according to the present disclosure, a “triaxial” DEP tweezers apparatus may be fabricated and employed to trap and move small objects in a fluid. In one exemplary implementation, a triaxial DEP tweezers apparatus has three conducting parts: a conducting tip (e.g., formed by an SPM or AFM tip itself), and two insulated conducting shells (i.e., an inner shell and an outer shell). In one aspect of this embodiment, RF voltages of opposite sign are applied to the conducting tip and the inner shell, while keeping the outer shell grounded. This configuration creates a quadrapole field with a very sharp zero in electric field amplitude a small distance away from the end of the tip. This zero can trap and move small particles that have a dielectric constant smaller than the fluid using negative DEP (nDEP). Important examples of such particles include, but are not limited to, nanotubes, semiconducting nanowires and nanocrystals in water. Accordingly, Applicants have recognized and appreciated that a triaxial tip configuration significantly facilitates the controlled assembly of sensors and electrical circuits based at least in part on nanoscale components (e.g., nanotubes, semiconductor nanowires, nanocrystals). In particular, the sharp electric field minimum provides an effective way to assemble nanoscale particles/components one at a time, as the large field around the minimum sweeps other particles/components away.

Since an SPM tip (e.g., an AFM tip) can be moved by a user, such a tip modified according to various inventive embodiments of the present disclosure to form a coaxial or triaxial DEP tweezers apparatus allows the user to manipulate individual trapped particles. For instance, the user can position the DEP tweezers apparatus near a target particle. The user can then trap the target particle by applying a voltage across the electrodes to create the dielectrophoretic trap. Then, the user can move the trapped particle to a desired location by repositioning the DEP tweezers apparatus to that location. The target particle can then be released at the desired location by turning off the voltage applied to the electrodes. In other implementations, similar principles can be applied so that the DEP tweezers apparatus itself is held constant while trapping the particle as a medium in which the particle is located is moved. The particle can then be released in a new region of the medium without moving the DEP tweezers apparatus. Additionally, a micromanipulator can be used to control a micromanipulator tool configured with electrodes arranged to support a dielectrophoretic trap when a voltage is applied across the electrodes. This dielectrophoretic trap can be used to trap and manipulate single cells or clusters of cells, as well as various nanoscale components.

Thus, one embodiment is directed to an apparatus comprising an elongated object forming a tip. The apparatus further comprises a first electrode that constitutes at least a first portion of the elongated object and has a first end proximate to the tip, and a second electrode that constitutes at least a second portion of the elongated object. The second electrode is insulated from the first electrode and has a second end proximate to the tip. The first end of the first electrode and the second end of the second electrode are positioned relative to each other so as to support a dielectrophoretic trap proximate to the tip.

Another embodiment is directed to a method of manipulating a particle or measuring at least one characteristic of the particle. The method comprises generating an electromagnetic field proximate to a tip formed by an elongated object, so as to support a dielectrophoretic trap proximate to the tip.

Another embodiment is directed to a method, comprising: A) generating a plurality of electromagnetic fields respectively proximate to a plurality of tips formed by a plurality of elongated objects, each elongated object comprising a first electrode having a first end proximate to a corresponding tip of the elongated object and a second electrode insulated from the first electrode and having a second end proximate to the corresponding tip; and B) positioning at least one of the plurality of tips and at least one storage medium such that the plurality of tips is proximate to the at least one storage medium so as to read information from and/or write information to the at least one storage medium based on the plurality of electromagnetic fields.

Another embodiment is directed to an apparatus, comprising: an elongated object forming a tip; a first electrode constituting at least a first portion of the elongated object and having a first end proximate to the tip; a second electrode constituting at least a second portion of the elongated object, the second electrode being insulated from the first electrode and having a second end proximate to the tip; and a third electrode constituting at least a third portion of the elongated object, the third electrode being insulated from the first electrode and the second electrode and having a third end proximate to the tip, wherein the first end of the first electrode, the second end of the second electrode, and the third end of the third electrode are positioned relative to each other so as to support a dielectrophoretic trap (2000) proximate to the tip (102).

Another embodiment is directed to a method, comprising: A) generating at least one electromagnetic field profile proximate to at least one tip formed by at least one elongated object, the elongated object comprising a first electrode having a first end proximate to the tip, a second electrode insulated from the first electrode and having a second end proximate to the tip, and a third electrode insulated from the first and second electrodes and having a third end proximate to the tip; and B) manipulating at least one nanoscale object based at least in part on the at least one electromagnetic field profile.

It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually exclusive) are contemplated as being part of the inventive subject matter disclosed herein. It should also be appreciated that terminology explicitly employed herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D are four views of an AFM tip configured as a dielectrophoretic tweezers according to one inventive embodiment of the present disclosure.

FIG. 2 is a view of the dielectrophoretic tweezers of FIGS. 1A-1D trapping a particle in a generated dielectrophoretic trap.

FIGS. 3A-3B are two views of a dielectrophoretic tweezers according to another inventive embodiment of the present disclosure.

FIG. 4 is a view of a dielectrophoretic tweezers of FIGS. 3A-3B trapping a particle in a generated dielectrophoretic trap.

FIGS. 5A-5B are two views of a dielectrophoretic tweezers comprising a hollow elongated object according to another inventive embodiment of the present disclosure.

FIGS. 6A-6B are two views of a dielectrophoretic tweezers comprising a hollow elongated object according to another inventive embodiment of the present disclosure.

FIGS. 7A-7B are two views of a dielectrophoretic tweezers comprising a central axis according to another inventive embodiment of the present disclosure.

FIGS. 8A-8B are views of two dielectrophoretic tweezers, each comprising a manipulator according to two implementations of the present disclosure.

FIGS. 9A-9D are views of four dielectrophoretic tweezers configured to allow the passage of radiation according to four other implementations of the present disclosure.

FIG. 10 illustrates a schematic diagram of a triaxial dielectrophoretic tweezers according to another inventive embodiment of the present disclosure.

FIGS. 11A and 11B illustrate perspective and cut-away front views, respectively, of a DEP tweezers array 500 according to one inventive embodiment of the present disclosure.

FIG. 12 illustrates simulated electric field profiles for a coaxial dielectrophoretic tweezers according to one inventive embodiment of the present disclosure.

FIG. 13 illustrates simulated electric field profiles for a triaxial dielectrophoretic tweezers according to one inventive embodiment of the present disclosure.

FIG. 14 illustrates trapping energy vs. axial and radial distance for dielectrophoretic tweezers according to one inventive embodiment of the present disclosure.

DETAILED DESCRIPTION

Following below are more detailed descriptions of various concepts related to, and embodiments of, inventive dielectrophoretic (DEP) tweezers apparatus and methods according to the present disclosure. It should be appreciated that various concepts disclosed herein, as discussed above and outlined further below, may be implemented in any of numerous ways, as the concepts disclosed herein are not limited to any particular manner of implementation. Examples of specific implementations are provided primarily for illustrative purposes.

FIGS. 1A, 1B, 1C, and 1D illustrate four different views of a DEP tweezers apparatus based on an AFM cantilever tip configuration, according to one embodiment of the present disclosure. FIG. 1A illustrates a lengthwise cross section of the cantilever configuration of the apparatus, which forms an elongated object 100, according to this embodiment, whereas FIGS. 1B, 1C, and 1D illustrate various close-up views of a portion proximate to a tip 102 of the DEP tweezers apparatus.

The DEP tweezers apparatus shown in FIGS. 1A, 1B, 1C, and 1D has an essentially coaxial electrode configuration and comprises a first electrode 104 constituting at least a first portion of the elongated object 100. The first electrode 104 has end 106 proximate to the tip 102. One or more constituent portions of the first electrode 104 can be made from virtually any conductive material or materials. In one exemplary implementation, the first electrode 104 is formed of highly doped silicon. In one aspect, the first electrode 104 is formed of an n-type silicon having a volume resistivity of between 0.01 and 0.025 Ohm-centimeters. In another aspect, the first electrode 104 has an overall shape of an AFM cantilever and is coupled to one potential of a voltage source 108 and an AFM base 110 that provides standard AFM functionality. In yet another aspect, the end 106 of the first electrode 104 may have a radius of less than about 10 nanometers.

The DEP tweezers apparatus shown in FIGS. 1A, 1B, 1C, and 1D further comprises an electrical insulating layer 112 surrounding the first electrode 104. In particular, the insulating layer 112 includes an end portion 114 that completely surrounds the end 106 of the first electrode 104. Thus, the end portion 114 insulates the end 106 of the first electrode 104 from any sample that may be proximate to the tip 102. In particular, because of this end portion 114 of the insulating layer 112, an electrical current is essentially precluded from flowing from the first electrode 104 to a particle/sample proximate to or in contact with the tip 102.

One or more constituent portions of the insulating layer 112 can be made from virtually any insulating material. In one exemplary implementation, the insulating layer 112 is made from a single layer of silicon dioxide. Such a layer can be formed around an n-type silicon first electrode 104 by oxidizing the first electrode 104 using well known silicon-based fabrication techniques. In various other implementations, a thickness of the insulating layer 112 may vary depending on the particular use of the apparatus and the range of voltages applied across the electrodes. Generally, the thickness is sufficient to prevent breakdown of the insulating layer 112 when the desired voltage is applied. In one implementation, a thickness of the insulating layer 112 made from silicon dioxide is about 100 nanometers.

As illustrated in FIGS. 1A, 1B, 1C, and 1D, the DEP tweezers apparatus of this embodiment also comprises a second electrode 116 constituting at least a second portion of the elongated object 100. The second electrode 116 is insulated from the first electrode 104 and has an end 118 proximate to the tip 102. In one aspect, the second electrode 116 constitutes (e.g., is disposed on) at least a portion of an outer surface 120 of the insulating layer 112, such that the insulating layer 112 insulates the second electrode 116 from the first electrode 104. One or more constituent portions of the second electrode 116 can be made from virtually any conducting material or materials. In one exemplary implementation, the second electrode 116 comprises two conductive layers, namely, an inner layer of chrome and an outer layer of gold. In various aspects, the respective thicknesses of these conductive layers can vary; in one implementation, a thickness for the chrome layer is about 10 nanometers, and a thickness for the gold layer is about 30 nanometers. These conductive layers can be formed on the outer surface 120 of the insulating layer 112 by well known techniques (e.g., vapor deposition) commonly employed in silicon-based fabrication processes.

In one aspect of the embodiment illustrated in FIGS. 1A, 1B, 1C, and 1D, the end 106 of the first electrode 104 and the end 118 of the second electrode 116 are positioned relative to each other so as to support a DEP trap proximate to the tip 102. As shown in FIGS. 1B and 1D, the end 118 and the rest of the second electrode 116 are arranged in a concentric manner around the insulating layer 112. This results in a coaxial configuration where the second electrode 116 extends along the length of the first electrode 104 (as discussed above, the insulating layer 112 also extends along this length to insulate the first electrode 104 from the second electrode 116). Furthermore, in one aspect, the end portion 114 of the insulating layer 112 protrudes from the end 118 of the second electrode 116 proximate to the tip 102 and insulates the end 106 of the first electrode 104 from any sample proximate to the tip 102. If the second electrode 116 is formed on the insulating layer 112 using vapor deposition, excess conducting material near the end 118 may need to be removed to allow this end portion 114 of the insulating layer 112 to protrude from the end 118 of the second electrode 116.

As illustrated in FIG. 1C, the insulating layer 112 also forms a spacing 122 between the end 106 of the first electrode 104 and the end 118 of the second electrode 116 that is suitable for supporting a significant DEP force proximate to the tip 102. In various implementations of DEP apparatus according to the present disclosure, the spacing 122 may range between about 500 micrometers and about 5 nanometers. This spacing 122 can affect the configuration of the electromagnetic field generated when a voltage is applied across the electrodes and thereby the strength of the resulting DEP force, as described below.

In one exemplary implementation, such a coaxial tip may be fabricated using a highly doped Si AFM tip as the first electrode 104, on which is grown approximately 100 nanometers of thermal oxide at approximately 1100° C. to provide the insulating layer 112. The second electrode 116 is provided by Au:Cr deposited in a thermal evaporator. The end of the tip may be opened with a focused ion beam (FIB) to produce the final tip geometry. These exemplary fabrication techniques may yield appreciably sharp tips, as thermal oxide layers on Si are conformal and can be grown a few nanometers thick, and very thin metal films can be deposited.

In one implementation, to produce a DEP trap using the tweezers apparatus illustrated in FIGS. 1A, 1B, 1C, and 1D, a voltage source 108 is coupled to the first electrode 104 and the second electrode 116. This voltage source 108 is configured to apply a voltage between the first electrode 104 and the second electrode 116 so that an electromagnetic field is generated proximate to the tip 102. As discussed above and explained in greater detail below, a DEP trap is thereby created proximate to the tip 102 when this voltage is applied. The magnitude and frequency of the applied voltage may vary depending on the application and type of particle to be trapped. In one aspect, the voltage source 108 is configured to have at least one of an adjustable amplitude and an adjustable frequency. As discussed below, the force associated with a DEP trap can be adjusted by varying at least one of the frequency and the amplitude of the applied voltage.

The force exerted on a particle in a DEP trap depends on the Clausius-Mossotti (CM) factor, a measurement of the effective permeability of the particle relative to the medium in which the particle is located. This factor varies between a value of 1 and −0.5 and is determined by the permittivity ∈_(m) of the medium in which the particle is located, the medium conductivity σ_(m), the particle permittivity ∈_(p), the particle conductivity σ_(p), and the frequency of the applied electromagnetic field ω. The Clausius-Mossotti factor can be determined by the following equation:

${CM} = {{{REAL}\left\lbrack \frac{\left( {\sigma_{p} + {\omega*ɛ_{p}}} \right) - \left( {\sigma_{m} + {*\omega*ɛ_{m}}} \right)}{\left( {\sigma_{p} + {*\omega*ɛ_{p}}} \right) + {2*\left( {\sigma_{m} + {*\omega*ɛ_{m}}} \right)}} \right\rbrack}.}$

When the Clausius-Mossotti factor is positive, a force pushes the particle towards stronger areas of the electromagnetic field. When the Clausius-Mossotti factor is negative, a force pushes the particle towards weaker areas of the electromagnetic field. The force applied to a particle in an electromagnetic field having a field strength E can be determined by the following equation, where ∈₀ is the permittivity of free space and a is the radius of the particle:

Force=3*π*a ³*∈₀*CM*∇(E ²).

Finite element methods can be used to determine the ∇(E²) term in this equation for a given electromagnetic field. This term varies based on the applied voltage and the configuration of the electrodes. As an example, consider a DEP tweezers apparatus as shown in FIGS. 1A, 1B, 1C and 1D having a spacing 122 of d between the end 106 of the first electrode 104 and the end 118 of the second electrode 116. A voltage with a magnitude V applied across these two electrodes generates an electromagnetic field proximate to the tip 102 with an estimated strength E=V/d. Without using finite element methods, the value of the term ∇(E²) can be reasonably estimated as V²/d³.

To illustrate the creation of a DEP trap, consider the apparatus displayed in FIG. 2. In FIG. 2, a target particle 124 is trapped in DEP trap 126 produced by electromagnetic field 128, which is generated by applying a voltage having magnitude V across the two electrodes 104 and 116. The frequency of this voltage determines the frequency of the electromagnetic field 128. Suppose that the electromagnetic field 128 is generated having a frequency ω such that the Clausius-Mossotti factor (CM) equals 1. Suppose also that target particle 124 has a radius a equal to d/2 (where d represents the spacing 122 indicated by FIG. 1C). From the force equation given above, and using the approximation ∇(E²)≈V²/d³, if the radius a of the target particle 124 is 5 micrometers and the magnitude V of the voltage applied across the electrodes 104 and 116 is 10 Volts, the force exerted on the target particle 124, which force creates the DEP trap 126, is approximately 1000 picoNewtons.

The force needed to effectively trap the target particle 124 varies depending on what other forces may be acting on the particle 124. Typically, between 10 picoNewtons and 1000 picoNewtons is sufficient to trap the particle 124. For example, a force just greater than 10 picoNewtons normally is sufficient to trap a protein, because typical forces that bind proteins together are on the order of approximately 10 picoNewtons. As forces acting on the particle 124 in the medium in which it is found increase, the DEP force needed to trap the particle 124 increases accordingly. Furthermore, external forces may act to remove the particle 124 from the DEP trap 126. For example, when the particle 124 is moved through a medium, such as by moving the DEP tweezers apparatus while the particle 124 is trapped in DEP trap 126, a drag force may act to remove the particle 124 from the trap 126. The force holding the particle 124 in the DEP trap 126 must be great enough to overcome this drag force and any other external forces that may be acting on the particle 124.

The medium in which the particle 124 is found also may play an important role in determining what frequency of voltage to apply across the first and second electrodes 104 and 116. A low frequency voltage is appropriately used to create a DEP trap 126 in a gas or vacuum. In some cases, a DC (i.e., zero-frequency) voltage is appropriate in these mediums.

However, in a fluid medium, a higher frequency voltage (e.g., from 10 kHz to greater than 1 MHz) may be more appropriate for creating the DEP trap 126. In some circumstances, a frequency into the GHz range is appropriate. A high frequency is desirable in some applications involving a fluid medium because ions in the fluid medium produce a fluid flow when a low frequency electromagnetic field is generated in the fluid. This fluid flow can disrupt the DEP trap 126. Generating a relatively higher frequency electromagnetic field helps prevent this fluid flow and leaves the DEP trap 126 effectively undisturbed.

Additionally, use of a high frequency electromagnetic field in a fluid prevents ions in the fluid from creating a shield around the DEP trap 126. At low frequencies, these ions may form a shield around the DEP trap 126, thereby blocking the DEP trap 126 from the rest of the fluid including the target particle 124. At higher frequencies, these ions are unable to move to form such a shield, and the DEP trap 126 is thereby free to trap the target particle 124.

In some implementations of the present disclosure, as illustrated in FIG. 2, the DEP tweezers apparatus may include a device 130 that can measure capacitance or conductance between the two electrodes 104 and 116. Since the capacitance and conductance vary based on a presence or an absence of the particle 124 in the DEP trap 126, the device 130 may be used to sense the presence or the absence of the particle 124 in the DEP trap 126. In one implementation of the present disclosure in which the DEP tweezers apparatus includes the voltage source 108 with an adjustable frequency or amplitude and the device 130, the frequency or amplitude of the voltage applied across the electrodes 104 and 116 may be varied while the device 130 measures the capacitance or the conductance across the electrodes. By measuring the capacitance or conductance across the electrodes over a range of frequencies or amplitudes, information about the trapped particle 124, including but not limited to information relating to the composition of the particle 124, can be determined.

The voltage source 108 of some implementations of the present disclosure may be configured to apply a current to a particle/sample 124 proximate to or in contact with the tip 102. For example, if either of the electrodes 104 or 116 of the DEP tweezers apparatus according to various embodiments discussed herein is put in contact with the particle/sample, voltage can be applied to that electrode thereby causing a current to flow to the particle/sample. In some embodiments, one of the electrodes is specifically shielded from a sample to prevent unwanted current flow (e.g., the first electrode 104 in FIGS. 1A-1D), but in those embodiments, a voltage can still be applied to the other electrode to cause a current to flow to the particle/sample. This process may be particularly useful for stimulating individual untrapped muscle or nerve cells located proximate to the tip 102 of the apparatus.

The various embodiments described above are only some of many possible embodiments for a DEP tweezers apparatus. Other possible embodiments may include tips of other types of SPMs, AFM tips, micromanipulator tool tips, sharpened glass tips, tips of other types of elongated objects, and the use of radiation with a DEP tweezers apparatus. Some of these other embodiments are discussed below.

FIGS. 3A and 3B illustrate two different close-up views of the tip 102 of another embodiment of a DEP tweezers apparatus according to the present disclosure. As discussed above with respect to other embodiments, the DEP tweezers apparatus shown in FIGS. 3A and 3B comprises a first electrode 104 constituting at least the first portion of the elongated object 100. The first electrode 104 has end 106 proximate to the tip 102. This embodiment of a DEP tweezers apparatus also comprises a second electrode 116 constituting at least the second portion of the elongated object 100. The second electrode 116 has end 118 proximate to the tip 102.

In the embodiment illustrated by FIGS. 3A and 3B, the first electrode 104 and the second electrode 116 constitute (e.g., are disposed on) opposing sides of the elongated object 100. An insulating gap 132 insulates the first electrode 104 from the second electrode 116. FIG. 4 illustrates the trapping of a target particle 124 via the DEP tweezers apparatus shown in FIGS. 3A and 3B, in a manner similar to that shown in FIG. 2. The dimensions of the insulating gap 132 shown in FIG. 3B depend on the desired voltage to be applied across the first and second electrodes and the desired characteristics of the electromagnetic field 128 to be generated proximate to the tip 102. Generally, the insulating gap 132 has dimensions suitable to support the DEP trap 126 proximate to the tip 102 and to prevent breakdown of the insulating gap when the desired voltage is applied across the first and second electrodes 104 and 116. In one implementation of this embodiment, the insulating gap will separate the first electrode 104 and the second electrode 116 by a distance between about 500 micrometers and about 5 nanometers.

FIGS. 5A and 5B illustrate two different close-up views of the tip 102 of another embodiment of a DEP tweezers apparatus according to the present disclosure. DEP tweezers apparatus configured according to this embodiment may be particularly useful as micromanipulator tools, including micropipettes.

The elongated object 100 illustrated in FIGS. 5A and 5B has a hollow core 134 that creates an interior surface 136 of the elongated object 100. The first electrode 104 constitutes the first portion of the elongated object 100 that, in this embodiment, corresponds to a first side 138 of the interior surface 136 of the elongated object 100. As in other embodiments discussed above, first electrode 104 has end 106 proximate to the tip 102. In the illustrated embodiment of FIGS. 5A and 5B, second electrode 116 constitutes at least a second portion of the elongated object 100 that, in this embodiment, corresponds to a second side 140 of the interior surface 136 of the elongated object 100. As in other embodiments discussed above, second electrode 116 has end 118 proximate to the tip 102.

In one implementation of this embodiment, the second electrode 116 is insulated from the first electrode 104 because the first electrode 104 and second electrode 116 are disposed on opposing sides 138 and 140 of the interior surface 136 of the elongated object 100 and are separated by at least a portion of hollow core 134. In one aspect of such an implementation, illustrated by FIGS. 5A and 5B, the insulating gap 132 ensures that the first electrode 104 and second electrode 116 are insulated from each other at the point where the first side 138 and second side 140 are closest to each other. The dimensions of the insulating gap 132 and the hollow core 134, in general, depend on the desired voltage to be applied across the electrodes and the desired characteristics of the electromagnetic field 128 generated proximate to the tip 102 (e.g., as discussed above in connection with FIG. 2). Generally, the insulating gap 132 and the hollow core 134 have dimensions suitable to support the DEP trap 126 proximate to the tip 102 and to prevent breakdown of the insulating gap 132 and the hollow core 134 when the desired voltage is applied across the first and second electrodes 104 and 116. In one implementation of such an embodiment, the insulating gap separates the first electrode 104 and the second electrode 116 by a distance between about 500 micrometers and about 5 nanometers.

Another embodiment of a DEP tweezers apparatus according to the present disclosure is illustrated in FIGS. 6A and 6B. In this embodiment, hollow core 134 forms the interior surface 136 of the elongated object 100. First electrode 104 constitutes the first portion of elongated object 100 that, in this embodiment, corresponds to at least a portion of an outer perimeter surface 142 of the elongated object 100. The first electrode 104 has end 106 proximate to tip 102. Second electrode 116 constitutes at least the second portion of the elongated object 100 that, in this embodiment, corresponds to at least a portion of the interior surface 136 of the elongated object 100. The second electrode 116 has end 118 proximate to the tip 102.

In one implementation of this embodiment, an insulating wall 144 of the elongated object 100 insulates the first electrode 104 from the second electrode 116. In one aspect of this implementation, as illustrated in FIGS. 6A and 6B, the first electrode 104 and second electrode 116 are arranged in a concentric manner. Generally, the insulating wall 144 has dimensions suitable to support the DEP trap 126 proximate to the tip 102 and to prevent breakdown when a desired voltage is applied across the first and second electrodes 104 and 116.

Still another embodiment of the present disclosure is illustrated in FIGS. 7A and 7B. In this embodiment, the elongated object 100 comprises a central axis 146 that passes though the elongated object 100. First electrode 104 constitutes the portion of the elongated object 100 that, in this embodiment, corresponds to at least a part of the central axis 146. Second electrode 116, in one implementation of this embodiment, constitutes the portion of the elongated object 100 that corresponds to the outer perimeter surface 142 of the elongated object 100. In another implementation, the second electrode 116 constitutes the portion of the elongated object 100 that corresponds to the interior surface 136. In one aspect of this embodiment, the resulting configuration may be such that the first electrode 104 and the second electrode 116 are essentially concentric and insulated from each other. The arrangement of the electrodes may vary but generally supports the DEP trap 126 proximate to the tip 102 and prevents breakdown when a desired voltage is applied across the first and second electrodes 104 and 116.

Any DEP tweezers apparatus embodiment may include at least one manipulator coupled to the tip 102, as illustrated in FIGS. 8A and 8B. In some implementations, the manipulator may be configured to move the tip 102 from one location to another location. As described above, if the tip 102 is moved from one location to another while the particle 124 is trapped in the DEP trap 126, the particle 124 will move with the tip 102. In some other implementations, the manipulator may be configured to hold the tip 102 in place and move the medium in which the particle 124 is located. As described above, if the medium is moved while the particle 124 is trapped, the particle 124 can be released in a new region of the medium. The manipulator may comprise any type of device capable of moving either the tip 102 or the medium, including, as illustrated in FIG. 8A, a SPM 148 and a piezotube 150, and, as illustrated in FIG. 8B, a micromanipulator 152.

As illustrated in FIGS. 9A, 9B, 9C and 9D, some embodiments of a DEP tweezers apparatus according to the present disclosure may be configured to allow radiation 154 to pass to or from a particle 124 trapped proximate to the tip 102. In one aspect of this embodiment, the interaction of radiation with a trapped particle, and the capability to direct radiation to or from the trapped particle via the DEP tweezers apparatus, may facilitate another methodology for particle characterization based on a particle's sensitivity and response to various wavelengths of radiation. To this end, the transported radiation 154 may comprise virtually any wavelength, including visible light, and may have a variety of bandwidths (e.g., from narrow-band/monochromatic to substantially broader band spectra).

In various implementations, a given DEP tweezers apparatus itself may be configured to direct first radiation to a trapped particle, and also direct second radiation reflected or emitted from the particle in response to the first radiation. Alternatively, a particle may be irradiated from a source not necessarily associated with the DEP tweezers apparatus, but radiation reflected by or emitted from the irradiated particle may be directed by the DEP tweezers apparatus (e.g., to some measurement or sensing device). Similarly, the DEP tweezers apparatus may be configured merely to direct radiation to impinge upon a trapped particle, and any other radiation emanated by the particle may be directed and/or measured by another means not necessarily associated with the DEP tweezers.

In one exemplary embodiment, the elongated object forming the DEP tweezers apparatus may be particularly configured so as to guide radiation. For instance, the elongated object may be configured so as to pass the radiation via at least one insulating medium between the first electrode and the second electrode. More specifically, one or more insulating media may be arranged so as to form a waveguide within the elongated object. In another embodiment, the elongated object may be hollow, and pass radiation via a hollow core. Alternatively, in yet another embodiment, the elongated object may include a fiber optic to guide the radiation.

More specifically, in one exemplary implementation illustrated in FIG. 9A, radiation 154 passes through hollow core 134 of elongated object 100 to and from the trapped particle 124. In another implementation, as illustrated in FIG. 9B, the elongated object 100 is configured to guide the radiation 154. In some implementations, as illustrated in FIG. 9C, the insulating layer 112 between the first electrode 104 and second electrode 116 may be configured to guide radiation 154 to and from the particle 124. In still other implementations, the elongated object 100 may include a fiber optic 156 to guide the radiation 154, as illustrated in FIG. 9D.

In another inventive embodiment of the present disclosure, a DEP tweezers apparatus may be configured to have a “triaxial” configuration, as shown for example in FIG. 10. A triaxial tip can provide a very sharp trap for semiconductor particles by using negative DEP in water. As illustrated in FIG. 10, a triaxial DEP tweezers apparatus according to one embodiment comprises three nested conical electrodes: a conducting core 104 (first electrode) having an end 106 proximate to a tip 102, an inner conductive shell (second electrode) 116 having an end 118 proximate to the tip 102, and an outer shell (third electrode) 1116 having an end 1118 proximate to the tip 102, wherein the respective electrodes are separated by insulating layers 112 and 1112. When RF voltages of opposite sign are applied to the core and inner shell electrode with the outer shell grounded, a quadrapole is created with magnitude |E| that falls off as 1/r⁴ at large distances. In one aspect, near the tip 102, the fields from the core and inner shell cancel to produce a very sharp minimum in |E|. The DEP potential around this minimum is sufficiently strong to trap semiconductor nanoparticles in water at room temperature to regions ˜5 nm in size, as discussed in further detail below.

In exemplary implementations, a triaxial DEP tweezers apparatus can be fabricated using a procedure similar to that for any of the coaxial DEP apparatus discussed above. In one implementation, triaxial DEP tweezers apparatus may be fabricated using atomic layer deposition (ALD) to deposit very thin conformal layers of metal (e.g. Pt) and insulators (e.g. Al₂O₃), that may be nested to make a coaxial or triaxial tip. The ability of ALD to make extremely thin insulators that don't leak electrically has led to its adoption by the semiconductor industry for the next generation of CMOS chips.

In yet another inventive embodiment of the present disclosure, multiple DEP tweezers apparatus according to any of the embodiments discussed herein may be employed together in a variety of geometric configurations or arrangements. Exemplary implementations of multiple DEP tweezers apparatus may include, but are not limited to, one or two dimensional arrays forming a spatial arrangement of tips, in which controllable local electromagnetic fields respectively may be generated proximate to the ends of the tips (i.e., generally confined to a small area proximate to each tip). In various aspects of such embodiments, hereinafter referred to generally as a “DEP tweezers array” or “DEP array,” each individual tweezers apparatus of the array may be operated individually and independently (e.g., via a voltage source 108, as discussed above in connection with FIGS. 2 and 4) to generate a controllable electromagnetic field, or groups of two or more tweezers apparatus may be operated together and simultaneously. Moreover, individual tweezers apparatus and/or groups of tweezers apparatus in the array may be operated in a series fashion and/or parallel fashion, so as to generate a variety of static or dynamic localized electromagnetic field patterns over an area generally encompassed by the array. In exemplary implementations, one or more voltage sources for individual or grouped members of a DEP tweezers array may in turn be controlled by a processor, computer, or other control circuitry to provide simultaneous or multiplexed variable amplitude/variable frequency voltage(s) to facilitate operation of the array.

FIGS. 11A and 11B illustrate perspective and cut-away front views, respectively, of a DEP array 500 according to one embodiment of the present disclosure. The exemplary DEP array 500 includes four DEP tweezers apparatus having a cantilever configuration constituted by elongated objects 100A, 100B, 100C, and 100D with respective tips 102A, 102B, 102C and 102D. It should be appreciated that a linear arrangement of four apparatus having a cantilever configuration is shown in FIGS. 11A and 11B primarily for purposes of illustrating one exemplary array 500, and that the disclosure is not limited in this respect, as arrays according to other implementations may have different numbers, arrangements, and configurations of DEP tweezers apparatus. In one exemplary implementation, DEP tweezers apparatus having a coaxial configuration as shown in FIGS. 1A-1D may be used in the array 500, whereas in other implementations, DEP tweezers apparatus having the configuration shown in FIGS. 3A and 3B, or configurations discussed in connection with other figures (e.g., a triaxial configuration as shown in FIG. 10), may be employed in the array 500.

In one exemplary application, DEP tweezers apparatus or a DEP array according to the present disclosure may be employed to facilitate nanofabrication processes including nanolithography and nano-manipulation (manipulation of nano-scale particles). The positioning of chemically synthesized nanoscale particles (nanowires, nanotubes, and nanocrystals) may be effectively controlled via the DEP tweezers apparatus and methods disclosed herein. Due to the small size of these particles, they are conventionally difficult to assemble into operational devices and circuits, particularly on the individual particle level. Conventionally, assemblies of nanoscale components generally are made by scattering nanowires over a substrate, and then attaching reflectors or leads where they have fallen. Nano-manipulation is a key enabling technology facilitated by the DEP trapping concepts disclosed herein for the assembly of nanoscale particle devices in a controlled manner (e.g., rapidly and precisely under computer control) from single devices to circuits, and eventually to wafer-level manufacturing.

The dielectrophoretic trapping techniques disclosed herein also may be employed to separate metallic nanotubes from semiconductor nanotubes based on the difference in their electrical conductance. Using the localized electric field at the tip of a DEP tweezers apparatus, this separation can be done on a single nanotube basis. Accordingly, via the DEP tweezers apparatus disclosed herein, individual particles can be identified and separated based on their dielectric properties. As discussed above in connection with FIGS. 2 and 4 with respect to particle characterization, a frequency of the RF field that forms the DEP trap may be varied (e.g., a frequency of the voltage applied to the electrodes may be varied), and frequency-dependent parameters of the trapped particle may be measured (e.g., a frequency-dependent capacitance or conductance) to determine a spectral response that may represent one or more particular characteristics of the trapped particle (e.g., metallic vs. semiconductor).

Both coaxial and triaxial DEP tweezers configurations may be employed to trap semiconductor nanoparticles/nanocomponents and to assemble them into structures. Applicants have recognized and appreciated that tip geometries may be designed to trap nanoscale particles at room temperature and hold them inside a nanoscale volume. A simple estimate of the radius r_(min) of the smallest particle that can be trapped is made by requiring that the particle's DEP trapping energy be greater than its thermal energy 2π∈_(m)r_(min) ³E_(rms) ²>k_(B)T with E_(rms) at the maximum value set by dielectric breakdown. In water r_(min)≈2 nm, small enough to trap a nanocrystal.

FIG. 12 presents simulated electric field profiles for coaxial DEP tweezers apparatus near the breakdown field, demonstrating the suitability of such apparatus for trapping of semiconductor nanoparticles in nanoscale volumes at room temperature. In FIG. 12, coaxial DEP tweezers apparatus with two geometries are considered. During fabrication, a focused ion beam can cut back the outer shell to completely expose the core electrode (FIG. 12, left top) or the focused ion beam can cut less deeply to simply open the outer shell leaving the core set back (FIG. 12, right top). More specifically, in FIG. 12, simulations of electric field magnitude |E| (V/m) vs. depth z (nm) are illustrated beneath the tip on-axis and radial distance r (nm) at z=5 nm with V_(tip)=5 V on the core electrode and a grounded outer shell, for two coaxial tip geometries: (left) a coaxial tip with core diameter 5 nm covered by 5 nm insulating shell, then a 5 nm metal film; (right) a coaxial tip with core diameter reduced to zero (modeling a finite radius core tip set back from the opening), covered by a 10 nm insulating shell, then a 5 nm metal film.

For the exposed core electrode on the left of FIG. 12, the peak electric field magnitude |E| at the core surface is large enough to trap a 10 nm diameter nanoparticle in oil at room temperature. As one moves radially outward from the tip at depth z=5 nm, |E| peaks at r=4 nm near the core edge, and the radius of the DEP trap is ˜5 nm. More sharply peaked |E| profiles can be achieved by using a set back core electrode, as shown in FIG. 12 of the right. In this case, |E| falls off quite rapidly with depth z and with radial distance r at z=5 nm, forming a maximum on axis at the end of the tip. The radial size of the trap for a 10 nm diameter at room temperature is nominally ˜2 nm, smaller than the particle size.

The simulations illustrated in FIG. 12 show that coaxial DEP tweezers apparatus according to various embodiments of the present disclosure are suitable for the assembly of semiconductor nanoparticles using positive DEP. The volume of the trap is quite small for an exposed core (left), but can be improved by setting the core back from the outer shell opening (right). The field |E| in the trapping region near the tip, is sufficient to trap nanoscale semiconductor nanoparticles and nanowires at room temperature.

FIG. 13 illustrates a simulation of an electric field profile for a triaxial DEP tweezers apparatus according to one inventive embodiment of the present disclosure, in which the triaxial apparatus has an outer radius of approximately 30 nm, with approximately 6 nm thick insulating layers 112 and 1112. Voltage sources 108A and 108B provide opposite potentials (e.g., plus and minus 3 volts) applied to the electrodes 104 and 116, with the outer electrode 1116 grounded. The field from the core and inner shell electrodes cancel just below the tip 102 to produce a very sharp minimum 2000 with |E|=0 at the center. This zero acts as a negative DEP trap for semiconductor nanoparticles in water at room temperature. Applicants have recognized and appreciated that being able to trap and assemble semiconductor nanoparticles in water is important, because it allows the use of selective molecular recognition techniques, as well as molecular binding to a substrate. The trap 2000 is very sharp, smaller than the size of the triaxial tip, and comparable to size the smallest nanoparticles. For some nanoparticles or nanowires, the spatial size of the trap in FIG. 13 is too small; it can be made larger to achieve stronger trapping by increasing the thickness of the shells.

The magnitude |E| of the electric field produced by the triaxial DEP tweezers apparatus is sufficient to trap semiconductor nanoparticles in water at room temperature (300 Kelvin), as shown by the simulations in FIG. 14. As in the simulations of FIG. 13, opposite RF voltages of plus and minus 3 volts are applied to the core and inner electrodes, with the outer electrode grounded. Plots of the ratio U_(DEP)/k_(B)T of the DEP energy U_(DEP) of a 5 nm radius InAs particle to k_(B)T are shown vs. depth z below the tip on axis, and vs. radial distance r at the depth z=12.5 nm of the minimum. A trap with strength U_(DEP)/k_(B)T>10 is strong enough to pick up and assemble nanoparticles at room temperature. The trap is quite small, radius 3 nm and depth 4 nm, for U_(DEP)/k_(B)T=10, truly nanoscale dimensions that are comparable in size to the nanoparticle being trapped.

The action of a triaxial DEP tweezers apparatus (i.e., the way that it picks up and places nanoparticles) is also very interesting. The sharp zero in |E| that traps a nanoparticle is surrounded by regions of strong |E| that push other nanoparticles away. Because the trap is comparable in size to the nanoparticle being trapped, it naturally selects one nanoparticle instead of pulling a cluster together. This is an advantageous effect for nanoassembly—i.e., selecting one nanoparticle and moving it through the fluid while sweeping the others away. This action permits heterogeneous assembly of a structure in a fluid that contains different types of particles. Throughout the assembly process, the triaxial DEP tweezers apparatus also can be used as a conventional AFM tip to image the structure being created.

In another exemplary application, DEP tweezers apparatus according to various embodiments of the present disclosure discussed herein may be configured to perform various biological application, such as electroporation of a cell proximate to the tip 102. The voltage source 108 of such implementations is configured to apply a properly timed pulse so that the electromagnetic field 128 generated thereby proximate to the tip 102 temporarily increases permeability of a cell membrane of the cell. Timing of the pulse is important, as is known in the art, since an overexposure to the electromagnetic field can cause serious cell damage. Generally, the pulse has a duration of between about 10 nanoseconds and about 10 milliseconds. While the cell membrane is in an increased state of permeability, it can be exposed to a desired substance (e.g., drugs, DNA, various reagents may be injected into the cell). The increased permeability allows the desired substance to pass through the cell membrane into the cell itself without the need to physically puncture the cell membrane. The desired substance can be delivered to the cell by the DEP tweezers apparatus itself if the elongated object 100 is configured as a micropipette or similar device (e.g., as discussed above in connection with FIGS. 5A, 5B, 6A and 6B). Other biological applications based on related concepts may include in vitro fertilization and tissue assembly.

In yet another exemplary application, the fields produced by a DEP array need not necessarily be used to trap particles, but alternatively may be used to facilitate data storage and retrieval. As discussed above, each DEP tweezers apparatus of an array can be configured and operated to produce a highly localized field that is confined to a small area proximate to the tip of the apparatus, and a collection of such fields may be used to read information from and/or write information to one or more storage media (e.g., read and write flash memory or ferroelectric bits). In general, the field confinement provided by the various DEP tweezers apparatus disclosed herein provides for a significantly smaller bit size than that achieved using conventional techniques (examples of mass-storage applications using conventional probe arrays and not employing DEP techniques are disclosed in U.S. Pat. No. 5,835,477, issued on Nov. 10, 1998 to Binnig et al., and entitled “Mass-Storage Applications of Local Prove Arrays,” which patent is hereby incorporated herein by reference).

Accordingly, the concepts disclosed herein relating to dielectrophoretic forces and DEP tweezers apparatus and arrays may be employed to realize significant improvements over conventional data storage and/or retrieval techniques such as those disclosed in the above-referenced patent. For example, in one method according to the present disclosure, a DEP array (specifically, the tips of such an array) is placed proximate to one or more storage media. One or more of the DEP tweezers apparatus constituting the array are then energized so as to generate one or more electromagnetic fields proximate to one or more tips of the array, and information is read from and/or written to the storage medium/media via the one or more electromagnetic fields thusly generated. In yet another exemplary application based on a similar approach employing multiple controllable localized fields, one or more electromagnetic fields thusly generated may be employed for exposing photoresist for subsequent development.

While several inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and/or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and/or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating items in a list, “or” or “and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of” or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.

In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03. 

1. An apparatus, comprising: an elongated object forming a tip; a first electrode constituting at least a first portion of the elongated object and having a first end proximate to the tip; a second electrode constituting at least a second portion of the elongated object, the second electrode being insulated from the first electrode and having a second end proximate to the tip; and a third electrode constituting at least a third portion of the elongated object, the third electrode being insulated from the first electrode and the second electrode and having a third end proximate to the tip, wherein the first end of the first electrode, the second end of the second electrode, and the third end of the third electrode are positioned relative to each other so as to support a dielectrophoretic trap proximate to the tip.
 2. The apparatus of claim 1, wherein the elongated object includes a scanning probe microscope (SPM) tip.
 3. The apparatus of claim 1, wherein the elongated object includes an atomic force microscope (AFM) tip.
 4. The apparatus of claim 1, wherein the first electrode, the second electrode and the third electrode are arranged in a concentric manner.
 5. The apparatus of claim 1, wherein respective spacings between the first end of the first electrode, the second end of the second electrode and the third end of the third electrode are suitable for supporting a significant dielectrophoretic force proximate to the tip.
 6. The apparatus of claim 1, further comprising at least one voltage source coupled to the first electrode, the second electrode, and the third electrode, wherein at least one voltage generated by the at least one voltage source creates an electromagnetic field proximate to the tip and wherein a force associated with the electromagnetic field provides the dielectrophoretic trap.
 7. The apparatus of claim 6, wherein the at least one voltage source is connected to the first, second and third electrodes so as to apply substantially equal and opposite voltage potentials to the first and second electrodes and a ground potential to the third electrode.
 8. The apparatus of claim 6, wherein the at least one voltage source is configured such that the generated voltage has at least one of an adjustable amplitude and an adjustable frequency.
 9. The apparatus of claim 6, wherein the force associated with the electromagnetic field is adjusted by varying at least one of the adjustable amplitude and the adjustable frequency of the at least one voltage source.
 10. The apparatus of claim 1, further comprising at least one manipulator coupled to the tip and configured so as to move the tip to at least one desired location.
 11. The apparatus of claim 10, wherein the at least one manipulator includes a scanning probe microscope.
 12. The apparatus of claim 1, in combination with at least one other apparatus according to claim
 1. 13. The combination of claim 12, wherein the at least one other apparatus includes a plurality of apparatus according to claim 1 such that the combination forms an array.
 14. The array of claim 13, wherein each apparatus of the array is essentially identical.
 15. A method, comprising: A) generating at least one electromagnetic field profile proximate to at least one tip formed by at least one elongated object, the elongated object comprising a first electrode having a first end proximate to the tip, a second electrode insulated from the first electrode and having a second end proximate to the tip, and a third electrode insulated from the first and second electrodes and having a third end proximate to the tip; and B) manipulating at least one nanoscale object based at least in part on the at least one electromagnetic field profile. 